1. Field of the Invention
The present invention relates generally to switch means used in digital computer systems for connecting components of the system to each other, and more specifically to switch means which allow a user of an input device to select one of a plurality of CPUs.
2. Description of Prior Art
In many circumstances arising during the manufacture, testing, and use of digital data processing systems, it is advantageous to be able to connect a single component of the system to one of a set of other components. For example, when testing CPUs, it is useful to be able to connect a single input or input-output device such as a terminal to more than one CPU. In the prior art, components have been connected by means of a patch panel: lines from the set of components are connected to sockets in the patch panel and a line from the single component is plugged into the socket for one of the set of components.
The patch panel is at best cumbersome, since the user of the single component must leave the component in order to switch to another of the set of components. At worst, the patch panel can be a major hindrance. For example, when a single terminal is used to test a set of CPUs, it is often necessary to switch frequently between CPUs, but not convenient to locate the patch panel near the terminal. Under such circumstances each switch between CPUs requires a long trip to the patch panel. In such an application, alternatives to the patch panel are complicated and expensive. For example, the terminal may be connected to each CPU by means of a relay and there may be means at the terminal for controlling the relays. By turning the relays on and off from the terminal, the user at the terminal can connect his terminal to a different CPU without going to a patch panel. However, the terminal must be provided with a means for controlling the relays and connections must be provided between that means and the relays themselves.